The two photos are a 750 Kw boiler switchboard in a 350 room hotel in Christchurch that I took today. The first photo is the left hand cabinet where the 630mm copper cables from a 1250A MCCB terminate onto those copper bars. The second photo is the right hand cabinet housing the MCBs and contactors that feed the elements in the storage tanks. The boiler panel has been in service for two weeks.
The 1250A MCCB is housed in the main switchboard in the same room about 3m away. The main switchboard is about 5m away from a 1000 kVA transformer. The fault level at those copper bars in the boiler panel is estimated at 22kA. The door to that cabinet had only one screw locking it and there was no shrouding over the copper bars. Lovely ! The hotel maintenance staff probably all have access to the boiler room. Eeeek ! ! !
The photos were taken on my phone ( yeah thats my phone cover obstructing the bottom of the first photo ). But you can see the orange 16mm flex cables all tucked into one lug. You'd think with bars that BIG the cables could have all been lugged individually. There a few other things wrong with the boiler panel, the 10kA rating of the MCBs is the next most glaring. A partial rebuild is now planned for this panel. Can anyone else see the other problems?:
Keir, I can see a few problems off-hand. Why weren't the studs sawn or ground off to make them shorter?. I agree with you on the part about the size of the busbars and the fact that the connections could have been better distributed along the bars. 630mm2 would suggest to me Aluminium cables, were AL/CU lugs used in the connections?. All I seem to see is Tinned Copper lugs a la Utilux. Are there washers under them nuts?, like shake-proof or the like?. Are only half of them MCB's on or were they installed up-side down?.
Before I touched anything I would ring the authorities to have a look and do something about the incompetent person who did this. The fact this is so close to a 1000kVA trannie is scary to say the least.
What is going on with those element circuits? It's 16mm to the contactors but looks like 6 mm going out to the elements. What's the size of the elements?
I can't see that the boiler draws anywhere near the 1250A rating of the MCCB on the main switchboard. I'm thinking more like 350A per phase, in other words 750kW total and not 750kW per phase. You need to check what it actually draws before redesigning the installation.
[This message has been edited by briselec (edited 05-13-2006).]
Briselec, 750kW is 1045A per phase. There are 30 x 25kW elements and the current on the 6mm cables has been measured at 35A, which the 6mm cable is good for but still should have been protected by a 40A breaker.
The rebuild will include: Replacing the copper bars with 4 x 315A MCCBs and replacing the 6mm cables with 10mm. Also Installing cooling fans with fault relays for the BMS.
At this stage there is no time to waste in a witch-hunt. The focus is on fixing the problem before something bad happens.
Trumpy, those studs should definitely have been shorter and half the MCBs have been switched off to lower the ambient temperature in the panel. Interestingly the boilers still maintain temperature with exactly half the elements switched off.
One small change is the 6mm element cables will have to now be upgraded to 16mm to allow for the grouping factor in the trunking.
Those element cables are also NOT V105 ( high temp) rated and they terminate straight onto the elements. But wait, theres more...... The elements aren't supported at both ends and they sag and rub against each other. But wait, theres more...... The water feed into the tank points straight into the elements with no baffle. When the pump switches on you can hear the elements rattling against each other.